The new study uses the MIT Integrated Global Systems Model, a detailed computer simulation of global economic activity and climate processes. It is the only model that also interactively includes detailed treatment of possible changes in human activities – such as the degree of economic growth, with its associated energy use, in different countries. Uniquely, the MIT model looks in great detail at the effects of economic activity coupled with the effects of atmospheric, oceanic and biological systems.
The difference in the 2009 and 2003 projections, the researchers say, is attributed to several factors based on new measurements and new analyses. They include improved economic modelling and newer economic data showing less chance of low emissions than had been projected earlier. Additionally, the new model takes into account a number of factors related to 20th century volcanoes, emissions of soot and deep-ocean temperature rises. The research has been published in the American Meteorological Society’s Journal of Climate.
Ronald Prinn, a co-author of the study, said the findings changed the odds on what could be expected if no policies were put in place to specifically reduce greenhouse-gas emissions. Without action, he said, “there is significantly more risk than we previously estimated. This increases the urgency for significant policy action.”
It is essential, according to Prinn, for the world to start making major changes — through adoption of significant national and international policies — as soon as possible. “The least-cost option to lower the risk is to start now and steadily transform the global energy system over the coming decades to low or zero greenhouse gas-emitting technologies,” he said.
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